Why is this the world's most valuable printed book?

Why has the Bay Psalm Book just become the world's most valuable printed book?

Why would someone (David Rubenstein to be exact) pay $14.2m for it?

The book symbolises America's pioneering spirit and desire for freedom

Is its age a factor? Printed in 1640, there is great pleasure in owning something that has been around for almost 400 years. Yet there are many much older books you can buy for less than $100. No, its age alone isn't the reason.

Beauty? Not particularly attractive.

Content? The text was not new, merely English translations of Hebrew psalms.

Condition? All copies of the book have been well thumbed by Puritan hands, including this one.

Rarity? Now we're getting somewhere. Around 1,700 first edition copies of the book were printed, in 1640. Just 11 are known to exist today. "Because the congregation for which it was created literally used the book to death, very few of the copies have survived," Derick Dreher, the director of the Rosenbach Library in Philadelphia, which holds another copy, told the BBC.

The remaining 10 are all housed in institutions, meaning this was the only example likely to appear for auction for the foreseeable future. The last one to appear for auction did so in 1947.

Yet rarity alone doesn't guarantee record prices. There are plenty of unique books out there that nobody wants.

So just why were collectors so desirous of the Bay Psalm Book?

As the first printed book in the US, the Bay Psalm Book has a unique position in the literary history of the country.

Yet there's more to it than that. It goes beyond literary history. It stands for something more important.

The book is symbolic of the founding of what would become the United States.

The Puritans who arrived at Massachusetts Bay from England in 1630 were searching for a new, better life. A life of freedom. That is a concept still held dear in the US.

"It was an act of independence going to Massachusetts and setting up their own society with their own version of Christianity, and I think you can draw a pretty direct line ultimately to the events of 1776," David Redden, the head of Sotheby's books department, told the BBC.

The book's symbolic nature explains why it surpassed the $11.5m figure achieved by the previous record holder for a printed book, a copy of John James Audubon's Birds of America. While "Birds" is a beautiful, rare and pioneering work, it lacks the historical importance of the Bay Psalm Book.

It's a concept to remember for your own collection: never underestimate the importance of the "big story" behind the artefact.